Cloth particularly for paper-manufacture machine

ABSTRACT

There is described a cloth for draining and drying paper webs, comprising a fabric formed by warp threads and weft threads. 
     Said cloth further comprises a top layer of interlaced lengthwise strips and weft threads, at least one upper weft thread part passing underneath one or a plurality of lengthwise strips, being connected to the fabric by at least one warp thread thereof, which has been passed between said upper weft thread part and the lengthwise strip or strips.

This invention relates to a cloth, particularly to a fabric or felt fordraining and drying paper webs in paper-manufacturing machines,comprising warp threads and weft threads which are woven together toform a fabric with a single layer or multiple layers, as well as to themethod for preparing such a cloth.

Cloths for drying paper webs in paper-manufacturing machines have beenknown for a long time. The moist paper web is caused to move over dryingdrums, on which said web is pressed by means of a drying cloth. Examplesof drying cloths having warp threads and weft threads so woven togetheras to form a single-layer- or multi-layer fabric have been disclosed forexample in W. KUFFERATH, Bindungssysteme von Papier-maschinensieben,Wochenblatt fur Papierfabrikation 5, 1982, pp.139 to 152.

A substantial problem with the drying cloths lies in providing apressing surface to be laid over the paper web which is as large and assmooth as possible, to improve the drying conditions of the paper web,and avoiding the cloth leaving traces printed in the dried paper web.

It has been tried to solve such problems by utilized in the weaving ofthe cloth warp threads with a cross-section which is not round, but tothe contrary rectangular (see for instance U.S. Pat. No. 4,290,209,published European Application No. 81 101584.1, or the cloth underTrademark PLANET, sold by the German Company Thomas Joseph Heimbach GmbH& Co). Such cloths, even if they have an enlarged contact area relativeto the usual cloths, do not solve completely satisfactorily the raisedproblems.

To solve said problems, there is provided according to the invention, acloth as described hereinabove, which further comprises a top layerwhich is formed by interlaced lengthwise strips and top weft threads,and at least part of the top weft thread passing underneath one or aplurality of lengthwise strips is connected to said fabric by at leastone warp thread thereof, which is passed between said top weft threadpart and the lengthwise thread or threads.

In an advantageous embodiment of the invention, the lengthwise threadsare arranged side by side, so as to cover substantially completely thefabric surface area.

In a preferred embodiment of the invention, the top weft threads are offlattened shape, preferably with a rectangular cross-section.

There is provided according to the invention, a method for preparing acloth of this kind, said method comprising forming a single-layer- ormulti-layer fabric by weaving warp threads and weft threads, whichmethod comprises the steps of forming simultaneously above said fabric,a top layer by interlacing lengthwise strips and top weft threads, andduring each top thread inserting, passing underneath same at least onewarp thread from said fabric.

Other details and features of the invention will stand out from thefollowing description, given by way of non limitative example and withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a cloth portion according to theinvention.

FIGS. 2 to 4 show lengthwise sections of various embodiments of thecloth according to the invention, FIG. 4 showing in section theembodiment as shown in FIG. 1.

FIGS. 5 to 7, and 8a, 8b, 9a and 9b show cross-sections along linesV--V, VI--VI, VII--VII, VIII--VIII, and IX--IX respectively in FIG. 2.

In the various figures, identical or similar elements are designated bythe same reference numerals in the various figures.

The cloth as shown in FIGS. 1 and 4, comprises a double fabric 1 formedby warp threads 2 and weft threads 3 which are interlaced in the usualway. Said threads are from a known material, and have properties andparameters which are conventional for cloths intended for drying paperwebs as will be known to those skilled in the art.

Said cloth further comprises a top layer 4 formed by lengthwise strips 5and weft threads 6, which are called here top weft threads.

In the embodiment as shown in FIGS. 1 and 4, the lengthwise strips arearranged side by side in such a way as to cover substantially completelythe surface area of fabric 1. The spacing D between the top weft threads6 is larger than the spacing d between the weft threads 3 of fabric 1.Each top weft thread 6 alternately passes over and underneath succeedinglengthwise strips 5.

Each part of top weft thread 6 which passes underneath a lengthwisestrip 5, simultaneously passes underneath one warp thread 2' from fabric1, said warp threads being shown in FIG. 4. Said warp threads are theones which retain the top layer 4 connected to said double fabric 1.

The lengthwise strips 5 are made from any suitable material for dryingcloths, as will be known to those skilled in the art. It is notablypossible to use a thermoplastic material. The width of the strips is notcritical, but it is preferred to have said width at least equal to thesum of the thickness of two adjacent warp threads and the mutual spacingthereof. Said strips may for example have a width of about 2.5 mm and athickness of about 0.1 mm.

The top weft threads 6 in the example as shown in FIGS. 1 and 4, aredifferent from the weft threads 3 of the double fabric 1. They mayhowever be identical in nature or shape, and they may thus also have around cross-section. It is however preferred to use top weft threadswith a flattened cross-section, for example a rectangular one.

In FIGS. 2 and 3 have been shown in lengthwise section, two otherembodiments of cloth according to the invention. Said embodiments differfrom the one as shown in FIG. 1 due to the supporting fabric 1 being asingle-layer fabric and not a double fabric any more.

For the clearness of the description, reference will be made to FIGS. 5to 7, and 8a, 8b, 9a and 9b to explain the method for preparing a clothaccording to the invention, said figures being cross-section views ofthe cloth as shown in FIG. 2, after bringing in each succeeeding weftthread. It appears from said figures that the supporting fabric 1 isformed by weaving as usual warp threads, eight of which are shown here(threads 11 to 18), which are moved between high and low positions withdetermined rates to form a shed, which will be called hereinafter lowershed. Four adjacent warp threads are covered by a single lengthwisestrip, and thus but two lengthwise strips 19 and 20 have been shown.They form a top warp covering the supporting fabric 1.

During four succeedng steps, a lower weft thread 21, 22, 23 and 24respectively, is passed through the lower shed, as it appears from FIGS.5 to 8a, and the lengthwise strips 19 and 20 are retained at the samelevel. FIG. 8a is a section view along line VIII--VIII in FIG. 2, afterbringing the lower weft thread 24 in, but before bringing the upper weftthread 25 in. During the following step as shown in FIG. 8b, the warpsare not fed on, the lengthwise strips 19 and 20 are so moved away as toform a shed, called hereinafter upper shed, and among the two warpthreads 14 and 18 passing over the lower weft thread 24, but warp thread24 is brought to a raised high position, as shown in said FIG. 8b, thatis directly underneath the lengthwise strip 19 lying in high position.An upper weft thread 25 is then also passed through the thus-formedupper shed, by passing thus underneath the warp thread 14 from thesupporting fabric 1, but along a path lying in a plane higher than theone followed by the weft threads 21 to 24.

After closing the upper shed by bringing closer the lengthwise strips 19and 20, the four following steps are indentical with the ones as shownin FIGS. 5 to 8a. It is indeed clear that the mutual position of thethreads and strips, in the fourth step from said following steps, shownin FIG. 9a, is identical with the showing in FIG. 8a. FIG. 9a is across-section view along line IX--IX in FIG. 2, after bringing the lowerweft thread 29 in, but before bringing the upper weft thread 30 in.During the following step, as shown in FIG. 9b, the warps are stoppedagain, the lengthwise strips 19 and 20 are spread in the oppositedirections to the position thereof as shown in FIG. 8b, and the warpthread 18 only is moved to a raised position. A weft thread 30 is thenpassed through the thus-formed upper shed, by passing thus underneaththe warp thread 18 from the supporting fabric 1, in the same plane asweft thread 25.

The embodiment as shown in FIG. 3 is very similar to the one as shown inFIG. 2, and only the passage order between the mutual high and lowpositions of the warp threads are different.

As it appears from FIGS. 2 and 3, the upper weft threads 25 and 30advantageously have a rectangular cross-section. This has the advantageof minimizing the contact area loss in the few spaced locations wherethe lengthwise strips pass underneath the upper weft threads.

The cloths according to the invention have relative to the known cloths,the substantial advantage of a marked increase in the possbile contactarea between the cloth and the paper web. Indeed, the presence of a toplayer comprised of wide strips lying side by side, and interlaced onlywith upper weft threads pertaining to said layer, which have preferablyalso a flattened cross-section, and this in relatively widely-spacedintervals, insures a smooth contact area with an extension neverobtained before. On the other hand, the connection formed by warpthreads from the underlying fabric, between said underlying fabric andthe upper weft threads, insures for said cloth a mechanical strength anda high capacity for pressing the paper web on the drying drums, withoutsimultaneously changing the extension of the contact area obtained withthe top layer, and the smooth shape thereof.

It must be understood that the invention is in no way limited to theabove embodiments and that any changes may be brought thereto withoutdeparting from the scope of the invention as defined by the appendedclaims.

It is possible to use for the supporting fabric, for example, as weftand warp threads, any type of thread usually used in drying cloths, andnotably yarns, multifilaments, monofilaments, mineral-fiber threads, orcoated threads.

The material or materials used for manufacturing the supporting fabricthreads, or the top layer threads and strips may be selected among thosematerials which are usually used for drying cloths, some of which maynotably be found in the previous publications as mentioned in thepreamble to this specification.

I claim:
 1. An improved papermakers fabric of the type having at leasttwo adjacent plies, each ply comprised of respective systems ofinterwoven warp and weft yarns, said plies are united by interweavingselected yarns of the respective systems, the improvementcomprising:said upper system having one set of yarns comprised ofinterwoven strips which substantially define the paper contact surfaceof the fabric, each of said interwoven strips having a width equal to atleast the width occupied by two yarns of the adjacent ply directlybeneath said strip and a thickness which is less than twenty percent ofthe width of said strip so as to define a width to thickness ratio forsaid strip of at least 5:1.
 2. The fabric of claim 1 wherein the yarnsinterwoven with said strips in the same system have a non-circular crosssection.
 3. The fabric of claim 1 wherein said strips run in thelengthwise direction of the fabric and the yarns interwoven with saidstrips in the same system have a non-circular cross section.
 4. Thefabric of claim 3 wherein the yarns interwoven with said strips are lessin number than the number of yarns in the adjacent ply which areparallel to said yarns.
 5. The fabric of claim 1 wherein said strips runin the lengthwise direction of the fabric and the plies are united byinterweaving lengthwise yarns of the adjacent ply system with thecrosswise yarns of the upper system.
 6. The fabric of claim 1 whereinsaid ratio is at least 10:1.
 7. The fabric of claim 1 wherein said ratiois at least 15:1.
 8. The fabric of claim 1 wherein said ration is atleast 20:1.
 9. The fabric of claim 1 wherein said ratio is at least25:1.
 10. The fabric of claim 1 wherein said strips run in thelengthwise direction of the fabric.
 11. The fabric of claim 10 whereinsaid ratio is at least 10:1.
 12. The fabric of claim 10 wherein saidratio is at least 15:1.
 13. The fabric of claim 10 wherein said rationis at least 20:1.
 14. The fabric of claim 10 wherein said ration is atleast 25:1.